1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, relates to a technique of forming a copper wire above a copper wiring.
2. Description of the Related Art
A description is given of a conventional semiconductor device with reference to the drawings.
In FIGS. 5 and 6, reference numeral 11 denotes a semiconductor substrate formed of, for example, a silicon substrate, and 12 denotes an interlayer insulating film formed on the semiconductor substrate 11. A lower-layer wiring portion 13 connected to a device element is formed in the interlayer insulating film 12.
Reference numeral 14 denotes an upper-layer wiring connected to the lower-layer wiring portion 13, and an insulating film 15 is formed so as to cover the upper-layer wiring 14.
In addition, a contact hole 16 for exposing a part of the upper-layer wiring 14 is formed in the insulating film 15, and a copper wiring 18 is formed above the insulating film 15 and inside the contact hole 16 with a barrier metal film 17 interposed therebetween.
More specifically, as shown in FIG. 5, the barrier metal film 17 is formed on the insulating film 15, and the copper wiring 18 is formed by a plating method on the barrier metal film 17 by using a resist film 19 as a mask. Then, a plated layer 20 is formed on the copper wiring 18 by using the resist film 19 as a mask. Incidentally, the plated layer 20 is a laminated film made of Ni and Pd.
Subsequently, as shown in FIG. 6, the resist film 19 is removed, and then a gold wire 21 is formed above the copper wiring 18 with the plated layer 20 interposed therebetween.
This technology is described for instance in Proceedings of 2001 International Symposium on Power Semiconductor Device & ICs, OSAKA “Lead Frame On Chip offers Integrated Power Bus and Bond over Active Circuit” pp. 6-68.
Recently, there has been a desire of implementing a semiconductor device using a copper wire, which is a low-cost material, instead of the gold wire described above.
However, in the semiconductor device structure described above, simply replacing the gold wire with the copper wire cannot ensure the reliability of the semiconductor device.
Specifically, copper is a relatively hard material (copper is three times as hard as gold). Accordingly, to prevent a bonding failure, wire bonding of a copper wire onto a copper wiring requires stronger ultrasonic waves and larger load than wire bonding of a gold wire. In this respect, even though the problem of the bonding failure is solved, experiments performed by the inventors showed an occurrence of a failure, such as a wiring separation or a crack in an insulating film formed under the copper wire.